Integrated circuits are implemented e.g. as system-on-chip on an ASIC; ASIC=Application Specific Integrated Circuit. An ASIC comprises special circuits, which are tailored to customers' wishes. These perform specific tasks. In telecommunications, for example, they are used for processing VoIP signals, DSL, ATM, SDH, SONET, UMTS, GSM, LMDS or ISDN signals; VoIP=Voice over Internet Protocol, DSL=Digital Subscriber Line, ATM=Asynchronous Transfer Mode, SDH=Synchronous Digital Hierarchy, SONET=Synchronous Optical Network, UMTS=Universal Mobile Telecommunication System, GSM=General System Mobile, LMDS=Local Multipoint Digital System, ISDN=Integrated Services Digital Network. They therefore serve for processing speech, data, video, Internet web pages, etc.
An integrated circuit has e.g. a special processor platform for implementing general but also application-specific tasks. This processor platform can be used for any applications; the same processor platform for example in DSL chips, ATM chips etc. It includes a processor and supplies computing capacity.
The processor platform has several components, some components being connected to a fast AMBA-AHB bus, e.g. a processor, a ROM controller, a RAM controller, and other components being connected to a slow AMBA-APB bus, e.g. an interrupt controller, a real time counter; ROM=Read Only Memory, RAM=Random Access Memory. The question of which component is connected to which bus depends on the access speed, the processing speed and the frequency of use of the component.
For some components, such as the ROM controller and the RAM controller, which are hereinafter referred to as modules, control registers are necessary. The usual solution provides for each module one or more control registers connected to the slow AMBA-APB bus.